The present invention relates to a method and apparatus for forming a magnetic component on a printed circuit board, such as a transformer or inductor.
The inventor""s U.S. Pat. No. 5,973,923, incorporated by reference herein in its entirety, describes a packaging technology for power converters and power magnetics, wherein the windings of a magnetic element or component are incorporated on layers of a multiple layer printed circuit board. This concept has provided many advantages, including reducing the printed circuit board surface area that must be devoted to magnetic circuit components, and reducing the reactance associated with the leads of the magnetic component. As just one example, a particularly advantageous application of the concept is described in the inventor""s U.S. Pat. No. 5,990,776, also incorporated by reference herein in its entirety. Notwithstanding the concept""s many advantages, however, there are some practical limitations.
One limitation is that, especially where the windings are long, there may need to be many layers in the printed circuit board to carry the windings. However, the cost to fabricate the printed circuit board generally increases dramatically with the number of layers, so that it is usually desirable to minimize this number.
Another limitation is that the resistance of the traces may not be sufficiently well controlled in the standard printed circuit board fabrication process for a given application of the magnetic component. Precise control of the dimensions of the traces is typically not critical in printed circuit board fabrication; however it may become critical where the traces are employed as part of the magnetic component, especially where the windings of the component are long and their combined resistance becomes appreciable.
Accordingly, there is a need for a method and apparatus for forming a magnetic component on a printed circuit board that provides for reducing the cost of fabricating the circuit board as well as the completed assembly, and that provides for increased control over the electrical resistance of the magnetic components.
The method and apparatus for forming a magnetic component on a printed circuit board of the present invention solves the aforementioned problems and meets the aforementioned needs by providing a printed circuit board having at least one inner layer having a trace that forms a winding of the magnetic component. At least one other winding of the magnetic component is provided by a supplemental length of wire formed in a loop that is disposed externally to the printed circuit board. Each type of winding provides advantages, and the proportion of each may be selected to optimize cost and circuit parameters.
Therefore, it is a principal object of the present invention to provide a novel and improved method and apparatus for forming a magnetic component on a printed circuit board.
It is another object of the present invention to provide a method and apparatus for forming a magnetic component on a printed circuit board that provides for decreasing the manufacturing cost of the printed circuit board as well as the completed assembly.
It is still another object of the present invention to provide a method and apparatus for forming a magnetic component on a printed circuit board that provides for increasing control of critical component parameters, such as the resistance of the magnetic component.
It is yet another object of the present invention to provide such a method and apparatus that provides for decreasing parasitic electrical effects.
The foregoing and other objects, features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the following drawings.